International Concrete Abstracts Portal

The use of the epoxy pressure injection technique to rehabilitate reinforced concrete beam-column joints damaged by earthquakes was investigated experimentally. Two full-scale exterior beam-column joint specimens were submitted to reverse cyclic pseudo-static displacements. The first specimen was typical of existing structures built in the fifties and sixties, in which the special seismic recommendations related to the spacing of lateral reinforcement in the beam, column, and joint were ignored. The second specimen was typical of new structures and incorporated full seismic details as prescribed in current building codes. The specimens were then repaired with an epoxy pressure injection technique. The repaired specimens were subjected to the same displacement history as that imposed on the original specimens. The results indicate that epoxy pressure injection was effective in restoring the strength, stiffness, and energy dissipation capacity of the specimens. For the specimen representing an older design, the strength and energy dissipation of the repaired assembly were increased as a result of the epoxy injection repair.

Existing beams coupling reinforced concrete walls are often found to be deficient. Common deficiencies include inadequate overall capacities, particularly shear capacities that are insufficient to develop flexural yielding of the beams. This research examines the use of steel plates to improve the shear resistance of reinforced concrete coupling beams in moderate seismic zones. Full-scale reversed cyclic loading tests of shear-deficient reinforced concrete coupling beams were carried out. The retrofit measures involved attaching thin steel plates on one side of the coupling beams to enhance their shear performance. A number of different ways of attaching the plate were investigated. Tests with the steel plate attached only with epoxy demonstrated a need for further connection to improve the hysteretic response. Additional specimens were constructed to investigate the influence of connecting the plate with both epoxy and bolting. The purpose of testing these retrofitted specimens was to develop a procedure for designing the plate connection details such that significant stresses are developed in the plate. The reversed cyclic loading responses of the retrofitted specimens are compared with a control specimen representing the deficient coupling beam before retrofit.

The seismic upgrade of the Hotel Utah was accomplished by constructing new concrete shearwalls to strengthen an existing historic building constructed in the early 1900s. Feasibility studies were performed to consider different methods of seismic upgrade; results indicated that new concrete shearwalls would provide the most economical method of upgrade without significant impact on the interior floor plan of the building. Construction of the new shearwalls was performed, for the most part, at the interior of the building which required special design and construction procedures.

Prior to the upgrading the seismic zoning of Massachusetts, not much attention was given to new or existing structures in the east coast with regard to seismic design and strengthening. Strengthening existing structures undergoing renovations has become mandatory for all government owned and operated buildings. This paper is the result of strength evaluation of two VA hospital buildings which are planned to undergo major renovations. Various options were considered for seismic strengthening of the two existing reinforced concrete frame structures, built in the 1930s without any earthquake load design considerations. Adding interior shearwalls, exterior buttresses, steel cross bracings, and base isolation proved to be complex, costly, and undesirable for architectural reasons. Use of peripheral shearwalls, attached to existing concrete frames was considered as a final solution for strengthening.

In 1987, testing began on a concept to use high strength fibers to retrofit columns to increase strength and ductility. The tests were completed on 14 columns at the University of California, San Diego. Columns were tested for confining the lap-splice flexural areas for circular and rectangular columns with increased strength and ductilities in testing of eight or more. Columns were tested for shear-flexural performance (with no lap-splice) with tested increased strength and ductilities of eight or more. The rectangular columns were wrapped in the shape of the rectangle successfully. The University of British Columbia in Vancouver used the wrap system for columns and pier cap retrofit and obtained a ductility of 12. Thirty-two field installations have been completed as of October 1994. Design recommendations and durability testing has been completed.